Indicator yarn construction

ABSTRACT

The present invention is related to a yarn construction comprising fibres A and at least one indicator fibre, wherein the indicator fibre comprises fibre B and an elemental metal at least partially coating the surface of the fibre B, wherein fibre A and fibre B are dissimilar ultra high molecular weight polyethylene (UHMWPE) fibres. The yarn constructions may be available in different forms, amongst others in ropes, straps, slings, fabrics and synthetic chains.

The present invention is related to a yarn construction comprisingfibres A and at least one indicator fibre, wherein the indicator fibrecomprises fibre B and an elemental metal at least partially coating thesurface of fibre B. Such yarn constructions may be available indifferent forms, amongst others in ropes, straps, slings, fabrics andsynthetic chains.

Yarn constructions from UHMWPE fibres such as ropes, slings, fabrics andsynthetic chains are used in a multitude of applications such aslifting, securing, protecting loads, goods or people. Failure of saidyarn constructions may result in substantial damage, replacement costsif not casualties.

Damages, especially when occurring through wear of the yarn constructioncan most often no be detected by contactless, visual inspection of theconstruction while a manual inspection is labor intensive and oftensubject to further deterioration of the yarn construction. Readiness forreplacement is hence difficult to identify, requiring an additionalsafety margin at increased cost.

Monitoring systems for yarn constructions, especially for ropes andcables, have been reported in the past. These systems aim at providingimproved detection and monitoring of the state of wear of the ropes andcables, allowing timely replacement.

Ropes and cables comprising conductive indicator yarns are for exampleknown from EP 2499291. EP 2499291 describes a conductive monofilament ormultifilament HPPE yarn and a rope or cable comprising the conductiveHPPE yarn, whereby the aging of the rope could be tracked by thedecrease of conductivity of the indicator yarn.

U.S. Pat. No. 8,360,208 describes monitoring the lifetime of a rope ofan aramid fibres with an indicator yarn. The indicator yarn consistingof carbon indicator fibres surrounded by aramid fibres with a highermodulus of elasticity than the aramid fibres. The construction providesan early deterioration of the indicator yarn, resulting in a failure ofa signal transmitted through the indicator yarn.

From EP 0731209 an layered aramid rope is known with carbon fibrespresent in each layer. The amount of snapped carbon fibres provides anindication of wear of the rope, assuring the residual load-bearingcapacity of the synthetic fibre rope.

Although the yarn constructions described above represent improvementsregarding lifetime monitoring of synthetic ropes and cables there is aconstant demand for further improvements, especially there is a need formonitoring systems with less complex yarn constructions and/or increasedadjustability.

Accordingly is it the aim of the present invention to provide a yarnconstruction with a further improved life-time monitoring. In particularit is an objective of the present invention to provide yarnconstructions with a less complex construction, such as a reduced numberof individual yarn components. A further objective of the invention maybe to provide a yarn construction with broader diversity of themonitoring system.

Surprisingly the aim of the invention is achieved by a yarn constructioncomprising fibres A and at least one indicator fibre, wherein theindicator fibre comprises fibre B and an elemental metal at leastpartially coating the surface of the fibre B, wherein fibre A and fibreB are dissimilar ultra high molecular weight polyethylene (UHMWPE)fibres.

By fibre is herein understood an elongated body, the length dimension ofwhich is much greater that the transverse dimensions of width andthickness. Accordingly, the term fibre includes filament, ribbon, strip,band, tape, and the like having regular or irregular cross-sections. Thefibres may have continuous lengths, known in the art as continuousfilaments or filaments, or discontinuous lengths, known in the art asstaple fibres. A yarn for the purpose of the invention is an elongatedbody containing many individual fibres. By individual fibre is hereinunderstood the fibre as such.

By yarn construction is herein understood a construction comprising orconsisting of at least two yarns such as for example a braid, a textile,a woven, a non-woven, a knitted, a twisted, laid, parallel or otherwiseformed structure.

In one embodiment of the present invention, the yarn construction suchas a twisted, laid, braid, a textile, a woven, a non-woven, a knitted, aparallel or otherwise formed structure can be combined with other typeof yarn. Preferably, the other type of yarn is a high-performance onesuch as for example, polyaramid yarns, polyamide yarns, teflon yarns,polypropylene yarns, etc.

The term yarn construction also encompasses an array of fibres such as aunidirectional (UD) monolayers. Unidirectional monolayers are producedby positioning yarns in parallel arrangement on a suitable surface andembedding the fibres in a suitable matrix material. The thus preparednetwork is unidirectionally aligned yarns in parallel to one anotheralong a common yarn direction.

Preferably the yarn construction according to the invention is a rope, asling, a fabric or a synthetic chain link. More preferably the yarnconstruction is a rope, wherein the rope contains a plurality of strandscomprising the ultra high molecular weight polyethylene (UHMWPE) fibresA and B.

UHMWPE fibres are herein understood to be fibres made from ultra-highmolar mass polyethylene and having a tenacity of at least 1.5,preferably 2.0, more preferably at least 2.5 or at least 3.0 N/tex.Tensile strength, also simply strength, or tenacity of fibres aredetermined by known methods as described in the experimental section.There is no reason for an upper limit of tenacity of UHMWPE fibres inthe rope, but available fibres typically are of tenacity at most about 5to 6 N/tex. The UHMWPE fibres also have a high tensile modulus, e.g. ofat least 75 N/tex, preferably at least 100 or at least 125 N/tex. UHMWPEfibres are also referred to as high-modulus polyethylene fibres or highperformance polyethylene fibres.

The UHMWPE yarns preferably have a titer of at least 5 dtex, morepreferably at least 10 dtex. For practical reasons, the titer of theyarns of the invention are at most several thousand dtex, preferably atmost 4000 dtex, more preferably at most 3000 dtex. Preferably the titerof the yarns is in the range of 10 to 10000, more preferably 15 to 6000and most preferably in the range from 20 to 3000 dtex.

The UHMWPE fibres preferably have a filament titer of at least 0.1 dtex,more preferably at least 0.5 dtex, most preferably at least 0.8 dtex.The maximum filament titer is at most 50 dtex, preferably at most 30dtex and most preferably at most 20 dtex.

The UHMWPE fibres may be manufactured according to any technique knownin the art, e.g. by melt, solution or gel spinning. Preferably theUHMWPE filaments are manufactured according to a gel spinning process asdescribed in numerous publications, including EP 0205960 A, EP 0213208A1, U.S. Pat. No. 4,413,110, GB 2042414 A, GB-A-2051667, EP 0200547 B1,EP 0472114 B1, WO 01/73173 A1, EP 1,699,954 and in “Advanced FibreSpinning Technology”, Ed. T. Nakajima, Woodhead Publ. Ltd (1994), ISBN185573 182 7.

UHMWPE is understood to be polyethylene having an intrinsic viscosity(IV, as measured on solution in decalin at 135° C.) of at least 5 dl/g,preferably of between about 8 and 40 dl/g. Intrinsic viscosity is ameasure for molar mass (also called molecular weight) that can moreeasily be determined than actual molar mass parameters like Mn and Mw.There are several empirical relations between IV and Mw, but suchrelation is dependent on molar mass distribution. Based on the equationMw=5.37*10⁴ [IV]^(1.37) (see EP 0504954 A1) an IV of 8 dl/g would beequivalent to Mw of about 930 kg/mol. Preferably, the UHMWPE is a linearpolyethylene with less than one branch per 100 carbon atoms, andpreferably less than one branch per 300 carbon atoms; a branch or sidechain or chain branch usually containing at least 10 carbon atoms. Thelinear polyethylene may further contain up to 5 mol % of one or morecomonomers, such as alkenes like propylene, butene, pentene,4-methylpentene or octene.

Fibre A in the context of the present invention is the base fibremeaning that fibre A represent the main, constituting, principal fibretype of the yarn construction. Preferably the yarn constructioncomprises at least 60% by weight fibres A, more preferably at least 80%by weight, most preferably at least 90% by weight. Consequently is theindicator fibre in the context of the present invention a minorcomponent of the yarn construction. Preferably the yarn constructioncomprises at most 40% by weight indicator fibres, more preferably atmost 20% by weight, most preferably at most 10% by weight, wherein allweight percentages are expressed as the weight of the respective fibreto the total weight of the yarn construction. The yarn construction mayfurther comprise auxiliary components to further enhance performance orgive it some additional properties, as would be known to a skilledperson.

In a further preferred embodiment, the yarn construction has a weightratio of indicator fibres to fibres A of less than 0.1, preferably lessthan 0.05, more preferably less than 0.02 and most preferably less than0.01. It was identified that larger ratios of fibre A to indicatorfibres results in increased life time of the yarn construction whilemaintaining the ability to reliably monitor the life time of theconstruction.

In a preferred embodiment, the yarn construction according to thepresent invention comprises at least one yarn A and at least oneindicator yarn, wherein the yarn A comprises UHMWPE fibres A and theindicator yarn comprises at least one indicator fibre. Preferably theyarn A substantially consists of UHMWPE fibres A and/or the indicatoryarn substantially consists of indicator fibres.

The indicator fibre and indicator yarn in the context of the presentinvention comprise UHMWPE fibres as described above of which the surfaceis at least partially coated with an elemental metal. Not limitingexamples of coated UHMWPE fibres and yarns are described in EP 2499291,which is incorporated herein by reference. The yarns disclosed in EP2499291 comprise an elemental metal forming a layer that adheres to thesurface of the UHMWPE fibres and covers at least partly the surface ofthe UHMWPE fibres. The elemental metal is deposited to the outer surfaceof a UHMWPE fibres via plasma sputtering. The indicator fibres andindicator yarns comprise an elemental metal once deposited to the yarnor fibres forms a layer that covers partly or fully the surface of thefibre or yarn. By partly is meant that the surface of the fibre or yarnpresents bare parts. The latter are parts of the surface of the fibre oryarn where elemental metal is not deposited to them. By fully, is meantthat the surface of the fibre or yarn does not present bare parts (asdefined herein above). Random and usually occurring localized layersurface defects such as pin holing, cratering, etc. may exist in eitherpartly or fully covered surface of an UHMWPE fibre or yarn.

The UHMWPE fibres B may be of continuous or discontinuous length, i.e.filaments or staple fibres. Though for some yarn constructions anindicator yarn with staple fibres B may be advantageous, for example foryarn constructions wherein fibre A is also a staple fibre, the yarnconstruction preferably comprises indicator fibres with continuousfilament fibre B. The inventors identified that such indicator fibreshave a wider range of application and in general deliver a better lifetime monitoring performance compared to staple indicator fibres.

An essential feature of the yarn construction of the present inventionis that the UHMWPE fibre A and B are different. Herein is understoodthat the fibre A and B are not the same, i.e. can be distinguished fromone another by at least one measurable feature. Such difference may forexample be the result of a different production process, such as usingdifferent UHMWPE, using different spin solvents, applying different drawratio during the spinning process, adding ingredients during theproduction process, etc. The skilled person will be aware of how toproduce fibres that differ from on to another.

In particular, such dissimilarity between the fibre A and B can beexpressed by the difference of a measurable fibre property. Suchproperty of a fibre can typically be expressed in a numerical value.Examples of fibre properties are filament titer, fibre tenacity, fibreelongation at break, fibre tensile modulus, intrinsic viscosity of theUHMWPE. Accordingly is a preferred embodiment of the present inventionthat the fibres A and B differ by at least one property, the propertybeing selected from the group consisting of filament titer, fibretenacity, fibre elongation at break, fibre tensile modulus and intrinsicviscosity of the UHMWPE.

The difference in the at least one feature may thus be the result of adifference in the production process and is hence an intended differenceof the fibres or yarns. By difference is herein not understood thedifferences that typically occur due to process fluctuations during aproduction process. Such differences resulting for example from afluctuation during the manufacturing process are in principle small andwould fall within the specifications of a commercial material. Incontrast are the fibres or yarns according to the present inventiondifferent to a point to be fibres or yarns that can be identified asindividual, separate products. Accordingly is it a preferred embodimentof the present invention that at least one ratio of a property of fibreB to the corresponding property of fibre A is at most 0.95, preferablyat most 0.9, even more preferably 0.8.

Alternatively the difference of at least one fibre property may beexpressed as a percentage difference. Such percentage difference iscalculated by dividing the difference between property of fibre A andthe corresponding property of fibre B by said property of fibre A,expressed in percent, herein referred to fractional difference orpercentage differences. The concerned properties for the fibres aremeasured in the same way and expressed in the same units.

By different property as used herein is meant that the value of therelevant property of fibre B is at least 5% lower than the value of thefibre A, more preferably at least 10%, even more preferably at least15%, most preferably at least 20%.

In one embodiment, the at least one difference between fibre A and fibreB may be the presence of fillers in fibre A and/or fibre B. Fillercomprising fibres are for example known from EP2074248 and EP2815006which are herewith included by reference. In a specific embodiment ofthe invention, the difference in fibre property is that the fibre Bcomprises more weight of filler than the fibre A. Preferably the fibre Bcomprises at least 2 wt %, more preferably at least 3 wt % and mostpreferably at least 4 wt % more filler than fibre A. All weightpercentages are expressed as at the weight of filler present in thefibre divided by the total weight of the respective fibre, including thefiller. It will be clear to the skilled person that the presence offiller in the fibre may affect further properties of the fibre and hencemore than one difference in fibre property can potentially beidentified. In a preferred embodiment, fibre A comprises less than 1 wt% of a filler, preferably fibre A comprises less than 0.5 wt % offiller.

By filler is herein understood particles present in the fibre differentfrom UHMWPE, in a preferred embodiment the filler particles have a highhardness. Accordingly is a preferred embodiment of the present inventiona yarn construction wherein the fibres B comprises filler with ahardness higher than the hardness of the fibre measured in the absenceof the filler. The hardness as expressed herein can be measured by knownmethods, preferably the harnesses are expressed and compared to oneanother in Moh's hardness.

Preferably the filler has a Moh's hardness of at least 2.5, morepreferably at least 4, most preferably at least 6. Typical fillersinclude, but are not limited to, metals, metal oxides, such as aluminumoxide, metal carbides, such as tungsten carbide, metal nitrides, metalsulfides, metal silicates, metal silicides, metal sulfates, metalphosphates, and metal borides. Other examples include silicon dioxideand silicon carbide. Other ceramic materials and combination of theabove materials may also be used.

The particle size, particle size distribution, particle diameter and thequantity of the filler are suitable to affect mechanical properties ofthe fibre. The filler particles may be of substantially spherical shape,with an average particle size substantially equal to the averageparticle diameter. For particles of substantially oblong shape, such asneedles or fibres, the particle size may refer to the length dimension,along the long axis of the particle, whereas the average particlediameter, or in short the diameter, refers to the average diameter ofthe cross-section which is perpendicular to the length direction of saidoblong shape.

In a preferred embodiment of the invention, at least part of the fillerparticles has an aspect ratio of at least 3, more preferably the fillersubstantially consists of particles having an aspect ratio of at least3. Such oblong filler particle shape showed to improve theresponsiveness of the indicator yarn to mechanical stress of the yarnconstruction. The aspect ratio of a filler particles is the ratiobetween the length and the diameter of the hard fibre. The diameter andthe aspect ratio of the hard fibres may easily be determined as reportedin EP2815006.

Preferably the fillers of the fibres are produced out of glass, amineral or a metal or are carbon fibres.

In one embodiment carbon fibres are used as the filler. Most preferablycarbon fibres are used having a diameter of between 3 and 10 microns,more preferably between 4 and 6 microns. Molded articles containing thecarbon fibres have increased electrical conductivity, and areparticularly suitable as the fibre for the indicator yarn for ropeconstructions with lengths of more than 100, 500 or even 1000 meter.

Furthermore, for the yarn construction UHMWPE fibre A with very goodperformance properties under stress can be used. Such performanceproperty can for example be creep, dynamic reverse bending capacity,elongation at break, abrasion resistance or tension-tension fatigue. TheUHMWPE fibre B comprised in the indicator fibre and/or the indicatoryarn will have a respective performance property under stress inferiorto that of the fibre A. The skilled person dealing with yarnconstructions for specific applications will be knowledgeable aboutdominant stress and failure mechanisms and will opt for a fibre A withhigh performance in said application. Accordingly will the skilledperson also be aware of fibres with inferior performance to be employedas fibre B for the indicator fibre. Accordingly is another embodiment ofthe present invention a yarn construction wherein the fibre B isinferior to the fibre A in terms of withstanding a stress.

In a yet preferred embodiment the inferiority of fibre B to fibre A isexpressed in that the flexural fatigue strength of the fibres B isinferior to the flexural fatigue strength of the fibres A, in that theelongation at break of the fibres B is inferior to the elongation atbreak of the fibres A, in that the resistance to abrasion of the fibresB is inferior to the resistance to abrasion of the fibres A, in that thetension-tension fatigue of the fibres B is inferior to thetension-tension fatigue of the fibres A or in that the creep rupture ofthe fibres B is inferior to the creep rupture of the fibres A. It wasobserved that flexural fatigue, yarn elongation, abrasion and creeprupture are dominant failure mechanisms of yarn constructions comprisinghigh strength UHMWPE fibres. Especially ropes or related constructionsare subject to fatigue due to repeated bending of the construction or toextension break due to high loads or prolonged operation under load.Failure of a yarn construction due to abrasion can be observed in yarnconstructions for protective covers but also in outer layers of loadbearing yarn constructions such as ropes and slings. Failure of yarnconstruction due to creep can be observed when the yarn construction isinstalled under a permanent tension. The present invention may provide amonitoring system for timely identifying the need for replacing a yarnconstruction before substantial damage occurs.

In the present invention withstanding a stress is expressed as aproperty of a fibre. It will be clear to the person skilled in the artthat in some cases a stress can only be applied and the resistance tosaid stress only be measured on a fibre present in a yarn or even in ayarn construction such as a rope. By the expression that fibre B isinferior to fibre A in terms of withstanding a stress is henceunderstood that fibre A and B will be compared to one another as fibres,as yarns consisting of the respective fibres or in yarn constructions ofsaid yarns of fibres.

The yarn construction may comprise other synthetic fibres next to theindicator fibres comprising fibre B and the fibre A. It was observed bythe inventors that the performance of withstanding a stress and/or theproperties of such other synthetic fibres is less critical for thefunctioning of the indicator yarn. In a preferred embodiment, theindicator yarn may comprise next to the elemental metal coated UHMWPEfibre B other synthetic fibres. Preferably the other synthetic fibreshave a respective property at least equal to the property of fibre Band/or a performance of withstanding a stress at least equal to theperformance of fibre B. Preferably the other synthetic fibre that may bepresent in the indicator yarn is fibre A or fibre B. Such yarnconstructions have proven to be less complex and may have increasedreliability of the service life indication of the yarn construction.

In a yet preferred embodiment of the invention the at least oneindicator fibre or indicator yarn is twisted, laid or braided to form anassembled yarn of the yarn construction. Said assembled yarn maysubstantially consist of indicator fibres or may be combined with othersynthetic fibres as described above to form the assembled yarn. In afurther preferred embodiment the indicator fibre or indicator yarn istwisted, laid or braided with fibre A, with fibre B or with fibre A andfibre B to form an assembled yarn. By assembled yarn is hereinunderstood an intermediate product comprising at least one yarn, the atleast one yarn has been processed alone or in combination with otheryarns.

In a further preferred embodiment, the yarn construction comprises aload carrying core which comprises at least one indicator fibre orindicator yarn. It is considered that especially the load carrying coresof yarn constructions, such as synthetic or hybrid ropes, slings orsynthetic chain links, are subject to damages occurring through wear ofthe yarn construction. Said cores are substantially buried within theyarn construction, covered by further yarn layers, metal wires, resinouscoatings etc. making a non-destructive, visible inspection utmostdifficult. The present invention is thus especially suitable formonitoring life-time of such yarn construction comprising a loadcarrying core.

The yarn construction may comprise a plurality of yarn layers or strandlayers. Each layer of the construction may include at least oneindicator fibre or yarn so that progressive degradation of the yarnconstruction can be monitored and replacement of the yarn constructioncan be estimated. Accordingly is a specific embodiment of the inventiona yarn construction comprising at least 2 indicator fibres or yarnsasymmetrically positioned within the yarn construction. By asymmetricalpositions is herein understood that the indicator fibres or yarns arelocated at positions that undergo a different stress under operation ofthe yarn construction. In the case the yarn construction is a rope,asymmetrically defines positions within the cross-section of the ropethat ore not equidistant from the center of the rope. In the case theyarn construction is a fabric, asymmetrically defines positions withinthe fabric that are not equidistant from a reference surface of saidfabric.

In a further embodiment, the yarn construction may comprise at least 2distinct indicator fibres or yarns. The 2 distinct indicator fibres havedistinct responsiveness to the stress applied to the yarn construction.Such distinct responsiveness may be achieved by indicator fibrescomprising different UHMWPE fibres B wherein the difference is expressedby a measurable fibre property as yet described for the fibres B. Thedifferent responsiveness of the indicator yarn may also be achieved byassembling the indicator fibres alone or in combination with furthersynthetic fibres through twisting or braiding.

The invention will be further explained with the help of the followingexample and comparative experiment.

Methods of Measuring

-   -   Intrinsic Viscosity (IV) is determined according to        ASTM-D1601/2004 at 135° C. in decalin, the dissolution time        being 16 hours, with DBPC as anti-oxidant in an amount of 2 g/l        solution, by extrapolating the viscosity as measured at        different concentrations to zero concentration. There are        several empirical relations between IV and Mw, but such relation        is highly dependent on molar mass distribution. Based on the        equation M_(w)=5.37*10⁴ [IV]^(1.37) (see EP 0504954 A1) an IV of        4.5 dl/g would be equivalent to a M_(w) of about 422 kg/mol.    -   Side chains in a polyethylene or UHMWPE sample is determined by        FTIR on a 2 mm thick compression molded film by quantifying the        absorption at 1375 cm⁻¹ using a calibration curve based on NMR        measurements (as in e.g. EP 0 269 151)    -   Tensile properties of fibres: tensile strength (or strength) and        tensile modulus (or modulus) are defined and determined on        multifilament yarns as specified in ASTM D885M, using a nominal        gauge length of the fibre of 500 mm, a crosshead speed of        50%/min and Instron 2714 clamps, of type “Fibre Grip D5618C”. On        the basis of the measured stress-strain curve the modulus is        determined as the gradient between 0.3 and 1% strain. For        calculation of the modulus and strength, the tensile forces        measured are divided by the titre, as determined by weighing 10        metres of fibre; values in GPa are calculated assuming a density        of 0.97 g/cm³.    -   Yarn's or filament's titer was measured by weighing 100 meters        of yarn or filament, respectively. The dtex of the yarn or        filament was calculated by dividing the weight (expressed in        milligrams) to 10; and yarns are determined by weighing 10 meter        of fibre or yarn.    -   Breaking strength and elongation at break of the rope        construction are determined on dry samples using a Zwick 1484        Universal test machine at a temperature of approximately 21        degree C., and at a speed of 100 mm/min.

EXAMPLES AND COMPARATIVE EXPERIMENT

Preparation of silver coated fibres and indicator yarns

Two types of silver coated fibres have been prepared according to themethod described in example 3 of EP 2499291. Silver coated fibres havebeen prepared starting respectively from the commercial UHMWPE yarngrades 3G12 1760 dtex and SK78 1760 dtex sourced from DSM Dyneema. Thesilver treatment was performed on a 220 dtex filament bundle resultingin silver coated filament bundle 1 (3G12) and 2 (SK78).

With these 2 silver coated filament bundles, 3 indicator yarns wereassembled:

Indicator yarn 1: the silver coated filament bundle 1 was assembled with20 tz from 8×220 dtex 3G12 80 tz to form a 1760 dtex silver coatedindicator yarn.Indicator yarn 2: the indicator yarn 1 was further assembled (4 st/cm,braided) with 3 3G12 1760 dtex yarns.Indicator yarn 3: the silver coated filament bundle 2 was assembled with20 tz from 8×220 dtex SK78 80 tz to form a 1760 dtex silver coatedindicator yarn which was further assembled (4 st/cm, braided) with 33G12 1760 dtex yarns.

Preparation of Yarn Constructions

A rope with a diameter of 21 mm has been prepared comprising the abovethree indicator yarns. The rope construction was 12×1×7×15×1760 dtexSK78. To avoid the three indicator yarns contacting each other, theindicator yarns were inserted in the S-strands, with an indicator freeS-strand between every indicator comprising S-strand. At the ends of theevaluated rope section, the indicator yarns have been exited from therope construction and connected through copper wires to an adjustablepower supply and LED indicator lights.

CBOS Testing

The rope with a maximum break load of 400 kN was subjected to a cyclicbending over sheave test until complete rupture with a stainless steelsheave of with a D/d of 20, a cycle frequency of 12 seconds and a bendzone of 420 mm under dry conditions. Cyclic Bending Over Sheave testmachine sourced from Lucassen Metaalbewerking b.v., NL.

During the test, the load applied to the rope was ramped up (100 cyclesat 10% MBL, 25 cycles at 15% MBL, 25 cycles at 20% MBL) to 25% of itsMBL. The rope failed after a total of 1907 cycles.

The degradation of the rope was monitored by the 3 LED connected to the3 indicator yarns. After 925 cycles the conductivity of indicator yarn 1dropped, indicating failure of said indicator yarn at 49% of ropelifetime. Indicator yarns 2 and 3 failed after 1876 and 1899 cycles,i.e. 98 and 99% of the rope lifetime respectively, unacceptably late asan indicator for premature replacement of the rope in a real lifeapplication.

1. A yarn construction comprising fibres A and at least one indicatorfibre, wherein the indicator fibre comprises fibre B and an elementalmetal at least partially coating the surface of fibre B, wherein fibre Aand fibre B are different ultra high molecular weight polyethylene(UHMWPE) fibres.
 2. A yarn construction according to claim 1 comprisingat least one yarn A and at least one indicator yarn, wherein the yarn Acomprises fibres A and the indicator yarn comprises the indicator fibre.3. The yarn construction of claim 1 wherein the fibres A and fibre Bdiffer by at least one property, the property being selected from thegroup consisting of filament titer, fibre tenacity, fibre elongation atbreak, fibre tensile modulus and intrinsic viscosity of the UHMWPE. 4.The yarn construction of claim 3 wherein at least one ratio of aproperty of fibre B to the corresponding property of fibre A is at most0.95, preferably at most 0.9, even more preferably 0.80.
 5. The yarnconstruction of claim 1 wherein at least fibre B comprises a filler andwherein fibre B comprises at least 2 wt % more filler than fibre Awherein wt % is the weight ratio of filler present in a fibre to thetotal weight of said fibre including the filler.
 6. The yarnconstruction of claim 5 wherein the fibre B comprises filler with ahardness higher than the hardness of the fibre measured in the absenceof the filler.
 7. The yarn construction of claim 1 wherein the fibre Bis inferior to the fibre A in terms of withstanding a stress.
 8. Theyarn construction of claim 7 wherein the inferiority is expressed eitherin that the flexural fatigue strength of the fibres B is inferior to theflexural fatigue strength of the fibres A, in that the elongation atbreak of the fibres B is inferior to the elongation at break of thefibres A, in that the resistance to abrasion of the fibres B is inferiorto the resistance to abrasion of the fibres A, or in that the creeprupture of the fibres B is inferior to the creep rupture of the fibresA.
 9. The yarn construction of claim 1 wherein the weight ratio ofindicator fibres to fibres A is less than 0.1, preferably less than0.05, more preferably less than 0.02 and most preferably less than 0.01.10. The yarn construction of claim 1 wherein the indicator fibre orindicator yarn is twisted, laid or braided with fibre A, with fibre B orwith fibre A and fibre B to form an assembled yarn.
 11. The yarnconstruction of claim 1 wherein fibre B is a continuous filament. 12.The yarn construction according to claim 1 being a rope, a sling, afabric or a synthetic chain link.
 13. The yarn construction according toclaim 12 comprising a load carrying core comprising at least oneindicator fibre or indicator yarn.
 14. The yarn construction of claim 1comprising at least 2 indicator fibres or yarns asymmetricallypositioned within the yarn construction.
 15. The yarn construction ofclaim 1 comprising at least 2 distinct indicator fibres or indicatoryarns.